Functional bacterial photoreaction centres with only one type of protein

The antenna system of Rhodospirillum rubrum. Detection of macromolecular constituents not stainable by Coomassie brilliant blue in solubilized preparations of the B880 complex

A solubilized preparation of the major Rhodospirillum rubrum antenna complex (B880) was obtained by a described procedure and its polypeptide composition was analyzed by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. Only two polypeptides of molecular weights close to 7000 were detected after staining the gels with Coomassie brilliant blue. However, several other constituents could be visualized by silver staining or by an immunochemical method. When the preparation was chromatographed on Sephacryl, some of the resulting fractions exhibited the characteristic B880 absorption spectrum and contained only the two proteins that were detectable with Coomassie brilliant blue. In those fractions the A 280/A 880ratio was 0.4, which indicated a significant improvement of the bacteriochlorophyll to protein ratio over the unchromatographed preparation (A 280/A 880=0.7). Other chromatography fractions lacked bacteriochlorophyll and contained a carotenoid which seemed to be bound to protein. The macromolecular constituents present in these latter fractions differed from those associated to the purified B880 complex in their electrophoretic moblities and/or in their staining properties. That suggested the possible existence of a carotenoprotein that did not result from the B880 complex upon loss of bacteriochlorophyll.

Transverse topography of the photochemical reaction center polypeptides in the Rhodopseudomonas capsulata membrane

The exposure of the three polypeptide subunits H, M, and L of the photochemical reaction center (RC) on both surfaces of the membrane of Rhodopseudomonas capsulata was studied by partial proteolysis with proteinase K and sodium dodecyl sulfate-polyacrylamide gel electrophoresis of of degradation products. The possible association of RC subunits with bacteriochlorophyll a and bacteriopheophytin was investigated by spectroscopical measurements. Chromatophores (inside-out oriented) and spheroplasts (right-side-out oriented), as well as purified, detergent-solubilized RCs and RCs reconstituted into phosphatidyl choline liposomes, were used. Subunit H of the RC was degraded to fragments with apparent MrS of 15,000 and 12,500, which were possibly derived from cleavage of a loop exposed on the cytoplasmic surface. Polypeptide M was digested at a comparable rate. The apparent Mr of M decreased by roughly 4,000 upon proteolytic cleavage. Subunit L was relatively insensitive to protease attack, except that a small peptide was clipped off. The primary donor P870 was also found to be only slightly affected proteinase K. All three RC subunits appear to be exposed on the chromatophore surface.